This invention relates to well arrangements for sub-surface fluid hydrocarbon production.
Techniques for hydrocarbon production are well known in the prior art, including conventional drilling techniques. The reference to xe2x80x9chydrocarbonxe2x80x9d herein is to fluid and gaseous hydrocarbons, such as crude oil and natural gas. However, under certain circumstances, conventional drilling techniques are not efficient to tap into a reserve of hydrocarbons. To tap into such reserves, xe2x80x9coil miningxe2x80x9d techniques have been developed, wherein a vertical or horizontal shaft is bored directly into, or in proximity to, the reserve. A drill room is excavated in the shaft, and horizontal wells, which may be slightly inclined, are bored from the drill room into the reserve. The wells allow for drainage of fluids into a common location, where the oil is transported by pump, or other device, to the grade surface.
The typical porous formation to which this method and device relate is a porous oil and gas bearing strata entrapped underground between a fluid impermeable cap rock above and a fluid impermeable stratum below. The typical desired fluid is hydrocarbon. The present invention relates to a method and a system which solves or avoids problems associated with prior art methods and systems used to recover desired hydrocarbons, such as oil or gas, from oil and gas bearing strata, which prior art is characterized by tunneling within or below the porous formation and drilling into the sands so that the desired fluid drains by the force of gravity into collection pits located on the floor of the tunnel.
Prior art methods and systems for using mine shafts or tunnels with oil drain pits for collecting oil drained form oil sands by the force of gravity have typically been called xe2x80x9coil-miningxe2x80x9d systems or methods. In one early method, tunnels were driven horizontally through the impermeable cap rock above the oil bearing sand and square pits were dug vertically through the tunnel floor to the oil bearing sands a few feet below. The oil drained into these pits and was lifted periodically by a pneumatic device into a pipeline extending to surface tanks. This system was used in the Pechelbronn field near Hanover, Germany and is disclosed in G. S. RICE, U.S. BUREAU OF MINES.
Another variation of this method is known as the Ranney oil-mining system and is disclosed in L. C. UREN, PETROLEUM PRODUCTION ENGINEERING: OIL FIELD EXPLOITATION, 3d Ed. McGRAW-HILL (1953). In this system mine galleries or tunnels are driven in impermeable strata above or below the porous formation of oil bearing sand and holes are drilled into the porous formation at short intervals along these galleries. Fluid is withdrawn through pipes sealed into the drilled holes and is pumped to the surface through a system of drain pipes in the galleries.
Another method which has been proposed for mining oil from partially drained oil bearing sands involves drilling a vertical mine shaft through the porous formation and drilling long slanting holes radially in all directions from the shaft bottom into the oil sands. The oil was to drain from the sand through the radial slant holes into a pit or sump at the bottom of the shaft and was to be pumped to the surface.
There are problems associated with these prior art oil-mining systems. For example, where high pressure gases may be present in the porous formation the prior art methods may be ineffective because either the gas will escape directly into the tunnels, galleries, or shafts or the gas will force itself directly into the collection pipe system, thereby leaving the liquid unrecovered in the porous formation.
As can be readily appreciated, the recovery of hydrocarbon using prior art techniques is a function of many factors, including the permeability of the strata in which the hydrocarbon is located (typically sand), the multi-phase presence of other fluids (e.g., water, brine), the viscosity of the hydrocarbon, and the pressures within the well bore and external to the reserve. The use of an insufficient number of wells will not maximally recover hydrocarbon from the reserve, whereas, an excessive number of wells may not be economical.
Enhanced horizontal drilling systems and methods encompass the production of crude oil from wells drilled from a subterranean production facility. This approach has the location of the well head below the oil reservoir to improve flow rate and recovery due to the consistent voiding of fluids by gravity flow within the well bore to the well head allowing well bore production pressure to achieve extremely low fluid pressure or even a vacuum of up to 15 PSI. This method increases oil recovery rate and factor, and lowers production costs.
The present method is production of shallow crude oil by way of long horizontal or near horizontal boreholes drilled and serviced from a subsurface workroom. The subsurface workroom serves as both the drilling platform and the place to which production is centrally accumulated from the wells. Oil is collected in a central facility and is then lifted to the surface utilizing pumps. The method allows for maximum control and range of borehole pressure, elimination of costly down-hole pumps and the introduction of production enhancing devices within the production stream such as in-hole injection of heated diluent.
When utilized in many low energy shallow oil fields the subject production method is projected to lower per barrel production costs, accelerate rates of oil recovery and increase total economic recovery when compared to other conventional production methods inclusive of horizontal and near horizontal wells. These cost savings are attributable to generally accepted engineering concepts that profess that oil production is subject to the following factors:
There is a direct proportional relationship between the amount of borehole surface area within the productive portion of the reservoir and the amount of fluid or gas produced.
Fluid and/or gas migration (flow) within the reservoir to the borehole is a direct result of the reservoir pressure exceeding the borehole pressure (differential pressure).
Fluid and/or gas migration within the reservoir to the borehole increases as differential pressure increases and declines as differential pressure declines.
As migration distances increase total economic oil recovery decreases.
Any production method that reduces the cost of the well bore surface area within the productive portion of the reservoir is desirable because the more borehole surface area within the production area the greater the recovery factor. Additionally any method that reduces migration distance to the borehole is desirable. The subject method increases borehole surface area and reduces migration distance within a given production area. The increased borehole surface area allows higher recovery rates and optimizes differential pressure. When compared with conventional horizontal drilling methods the present method may save up to 60% of the combined capital and operations cost to produce a like amount of oil or gas for a like period of time. However, the subject method also may increase the recovery factor by up to 100% resulting in a dramatic increase in resource efficiency.
The potential savings offered by the method result from the following factors:
The borehole is located almost entirely within the productive portion of the reservoir.
The borehole is all drilled from a central location eliminating the cost of replicated support apparatus and the cost to break down, move and erect the drill rig. Cost is further reduced by the ability to use inexpensive proven drilling technology.
Conventional boreholes are not produced in a static environment. As reservoir pressures approach zero the well has to be more frequently evacuated because the fluid column within the borehole more quickly reaches equilibrium with the reservoir pressure; hence flow stops. Because the well bore is drained to a central collection point the method allows for static production conditions down to 15 PSI vacuum pressure hence total economic recovery is increased.
The production geometry reduces the migration distance; hence total economic recovery is increased.
Consolidation of surface facilities further reduces operating expenses.
environmental savings due to improved monitoring and centralization of production facilities making discovery and remediation of discharge events more effective.
Conventional vertical and horizontal wells require down-hole pumps to lift the oil when fluid column from the reservoir to the surface exceeds reservoir pressure. (This is the case at some point in the life of all wells.) The maintenance of the down-hole pumps is expensive. Frequent pulling operations utilizing work-over rigs to retrieve and replace the pumps are required to keep the wells producing. These pulling operations are quite expensive and contribute significantly to operating costs and increases down-time and lost revenue. The subject method requires no down-hole pumps or other down-hole servicing. All pumping is done through large reliable and efficient pumps centrally located in the subsurface drill room that are easily serviced.
The following forecast environmental benefits are derived from the production methods:
1. Reduction of surface disturbance by 90%+.
2. Consolidation of production facilities and reduction of surface communication.
3. Reduction in reclamation effort.
4. Elimination of cross-communication of fluids within the well bore as wells cross various formations.
5. Dramatic increase in recovery per acre results in improved trade-off when considering surface disturbance.
6. Central drilling location provides improved economics of scale for more effective treatment of drilling wastes and by-products.
7. Central location of all facilities makes twenty-four hour monitoring of entire production facility economically possible. Non-stop monitoring allows for quicker discoveries of leaks, less environmental damage and lower cost environmental remediation.